Disclosed herein are a tire pressure estimating apparatus and a tire pressure estimating method thereof. The tire pressure estimating apparatus according to an embodiment of the present disclosure includes an input unit that receives a current wheel speed signal sensed by a sensing device, an analysis unit that analyzes a suspension resonance frequency value according to a current load value based on the input current wheel speed signal, a determination unit that determines whether the current load value is increased for a certain period of time, a compensation unit that compensates for a tire relative dynamic radius difference value and a tire relative air pressure difference value according to a load increase by applying a load compensation model to a tire dynamic radius analysis model, when the current load value is increased for the certain period of time, and an estimation unit that estimates a final tire pressure value based on the compensated tire relative dynamic radius difference value and tire relative air pressure difference value.